The broad objective is the development of new and practical radiopaque dental resins. A number of useful resins have been developed based on the corporation of X-ray absorbing metal salts in monomers via cation-chelating groups. This approach evolved to include organometallic compounds, monomers and polymers in which the metal is covalently bound to the organic structure. These resins have additional processing and performance advantages and, when combined with phosphoryl-monomers, they can be made to develop dentin adhesive properties as well. It is the intention to explore the practical possibilities inherent in these advances. Specifically, the aims are: 1. Complete the development of a practical radiopaque prosthetic resin system using copolymerizable organometallics. 2. Expand the scope to include radiopaque root canal sealants, dentin adhesives and resin cements that are adherent to dentin. 3. Synthesize organometallic monomers and resins in support of 1 and 2. 4. Evaluate the performance and biocompatibility properties of fully formulated radiopaque resins designed or prosthetic, bonding and endodontic applications. To obtain reactive, radiopaque, adhesive resin components we wiU: optimize the yield of the bismuth-styrene derivatives, synthesize Sb-styrene monomers, synthesize the Bi, Ti, Zr, and Hf derivatives of vinylbenzyl chloride, homopolymerize and copolymerize these monomers with dental acrylic monomer systems and phosphonate-monomers, develop crosslinking agents based on trivinylbenzyl- and trivinylphenyl-bismuth, develop additional organometallic monomers and resins which also contain phosphonate moieties, develop low M.W. oligomers and prepolymers from the above compounds for formulating low viscosity resins having minimal polymerization shrinkage, and combine chelated heavy metal salts with organometallic monomers and copolymers to increase radiopacity beyond that obtainable with either alone. Final improvements in prosthetic resins will be accomplished by using organometallic monomers such as p- diphenylbismuth-styrene to impart radiopacity. Resin cements and endodontic sealants will be developed that are both adhesive to dentin and radiopaque, by combining the phosphonate compounds with organometallic and/or chelate-metal monomer and polymer compounds. Finally, a battery of in vitro physical, mechanical and biological safety tests will be conducted on selected materials in order to predict their processing and performance characteristics for prosthetic, restorative and endodontic applications.